The problem can arise when you disconnect the factory boost solenoid. The turbo can actually spool to 14psi at part throttle (normally Subaru limits this to ~8-9 psi). This can cause the EGT to increase (some people but now all have reported this problem).
Many people have changed their driving style style to compensate for this. I on the other hand, want to tune this out with the proper tools (albeit at a reasonable price). Because I want to be able to turn up boost for fun to 16psi, and down for the street, I need an adjustable BC. MBC's don't allow enough tuning.
I am thinking if I do a proper RPM map and overboost control, I can satisfy the req without going to a Link (which is over kill for what I want). The factory full map runs rich, so I am hoping I can find a happy median with boost and the fuel mixture.